The invention relates to first-in-first-out (FIFO) buffers and, more particularly, relates to systems and methods for handling underflow and overflow in a FIFO buffer of a digital cordless telephone handset unit or base set unit.
Digital cordless telephones typically consist of two separate units, a base set unit that generally remains at a particular location and a handset unit that is portable in relation to the base set unit. In operation of such a digital cordless telephone, the base set unit and handset unit communicate by radio frequency various protocols and data signals between the units. Typically, the base set unit and the handset unit are synchronized by making one unit, often the handset unit, a timing slave to the other unit, the base set unit in that instance, the master timer. Although one unit is a timing slave to the other unit, each unit may have its own internal clock, for example, derived from a crystal of the respective unit.
In the related applications cross-referenced above and in other related digital cordless telephone designs, the slave unit acts as a slave to the other master unit in normal operation, however, upon a fade of radio frequency signals communicated by the units, each unit commences operations during the fade according to its own internal clock.
The results of such operations during the fade is that the slave unit, upon losing the timing signal from the master unit, commences operation during the fade via the internal clock of the slave unit. The internal clock will, in that instance, have a relationship with the timing of the master that is different than the relationship prior to the fade. This presents a problem to system synchronization because mechanisms for synchronizing the slave unit timing to that of the master unit requires some timing signal from the master unit in order to achieve the synchronization. That problem is evident, for example, when master and slave timing relationship of communicating units are disturbed to such extent that the normal synchronization scheme of master and slave cannot maintain appropriate synchronization.
An example of such an instance of disturbed master and slave timing relationship is the drift of master and slave timing due to signal fades. As signal fades occur and timing signal communications are momentarily lost during the fades, drift may occur between one unit's timing and that of the other unit. As the drift grows because of recurring fades, the drift may present a situation in which the drift offset is so large that it involves a complete cycle of timing of a unit. When that occurs, communicated data between the units may be lost, resulting in invalid or otherwise inappropriate communications between units.
Embodiments of the present invention provide systems and methods for accounting in communications between communications units for drift of master and slave timing that results in loss of complete timing cycles. The present invention is clearly a significant improvement in the art and technology.